Seven tiny teeth tell the story of an ancient monkey that made a 100-mile trek across the ocean between North and South America into modern-day Panama—the first fossil evidence for the existence of monkeys in North America.

The find provides the oldest fossil evidence for the interchange of mammals between South and North America and challenges long-held views of South America as an island continent that evolved in isolation before the Isthmus of Panama was formed and animals began crossing between the continents about 3.5 million years ago.

Scientists uncovered the teeth belonging to the 21-million-year-old primate during recent excavations related to the expansion of the Panama Canal. (Credit: Florida Museum of Natural History)

As reported in the journal Nature, scientists uncovered the teeth belonging to the 21-million-year-old primate during recent excavations related to the expansion of the Panama Canal. The new genus and species, dubbed Panamacebus transitus, received its name from the Latin word transit, meaning crossing.

It is somewhat of a mystery how P. transitus traveled across the sea dividing North and South America during the early Miocene. It may have swum across, but this would have required covering a distance of more than 100 miles, a difficult feat for even the most talented long-distance swimmers. It’s more likely P. transitus unintentionally rafted across on mats of vegetation, much like their ancestors who probably made their way from Africa to the New World in a similar fashion.

The unearthing of P. transitus—which probably looked a lot like a capuchin or “organ grinder” monkey—adds a new chapter to the “utterly bizarre” history of New World monkeys, says Jonathan Bloch, curator of vertebrate paleontology at the Florida Museum of Natural History at the University of Florida.

“Somehow they made a transoceanic journey from Africa, then they dispersed throughout South America. Now we see that they, as far as we know, are the only mammal that successfully crossed the early Miocene Central American Seaway into present day Panama. So how were monkeys able to do this?

The new genus and species, dubbed Panamacebus transitus, probably looked a lot like a capuchin or “organ grinder” monkey. (Credit: Florida Museum of Natural History)

“Hopefully future fossil discoveries will help us better understand this extraordinary history.”

The ocean-faring monkey suggests the modern diversification of New World monkeys happened in the ancient tropics. The surprising discovery of the first fossil monkey from North America extends the record for the beginning of the modern diversification of New World monkeys by more than 5 million years, Bloch says.

“Uncovering a monkey this old in Central America, at the southern-most point of the North American landmass, is similar in some ways to finding Homo erectus, an extinct human ancestor known only from Africa and Asia, in Australia.”

It also provides fossil evidence for a pattern previously documented by molecular scientists who have suggested for some time that a variety of animals, including amphibians, reptiles, freshwater fish, and insects made ocean crossings between North and South America during the early Miocene.

New World monkeys today are restricted to tropical forests from Brazil to southern Mexico, but during the early Miocene they were found throughout South America, including some of the continent’s highest latitudes. The new primate raises the question of why these monkeys are not found farther north once they crossed the seaway into Panama, says coauthor Aaron Wood.

“While the fossil mammals found with P. transitus include horses, camels, and squirrels that look like what paleontologists have found in the early Miocene of Mexico, Texas, and Florida, the new monkey was limited to the southernmost point of the continent,” says Wood, who discovered the teeth as a postdoctoral researcher in 2012 and is now a paleontologist at Iowa State University.

“The ancient South American-derived forests found in Panama were absent in northern Central America at the time, preventing monkeys from moving north, even though climate and geographic barriers like oceans did not wholly restrict their northward movements.”

Micro-CT scans of the fossil specimens are available for viewing in 3D or for 3D printing. Other researchers from the University of Florida, Iowa State University, Duke University, the Smithsonian Tropical Research Institute in Panama, Universidad de los Andes in Colombia, and the New Mexico Museum of Natural History and Science are coauthors of the study.